466 



46 



sect's body, called spiracles. The spii*acles or breatliing-i)ores can be 

 easily seen along the sides of all caterpillars Avhich are not too densely 

 covered with hairs. In the perfect or winged state of insects the 

 branches of the air tnbes are dilated into a great nnmber of little ves- 

 sicles or air bladders, wliich render their bodies lighter, and thus faciU- 

 tate their Hight. 



In some aquatic larva", the tracheae project from the liody in the form 

 of little tufts, analagous to the gills of fishes. The aquatic beetles are 

 under the necessity of rising to the surface, at intervals, for air, in a 

 manner similar to that of the aquatic mammalia, the whales and the 

 dolphins. 



THE DIGESTIVE OU NUTETTIVE SYSTEM. 



The digestive apparatus of insects, 

 like that of other animals, consists of 

 an elongated tube called the aliment- 

 ary canal, extending through the body, 

 and having a number of anlargements 

 in its course, and in many insects i)re- 

 sents a particular resemblance to the 

 digestive a[)[)aratus of birds. First, 

 there is a short, straight (esophagus 

 or gullet ; this expands into a nnich 

 larger cavity resembling the crop ; 

 then follows a smaller muscular part, 

 analagous to the gizzard ; and next, a 

 much larger and longer canity which 

 is the true digestive stomach ; this be- 

 comes contracted into the intestinal 

 canal, which sometimes runs nearly 

 straight through the body, and in other cases is more or less convolu- 

 ted ; the intestine enlarges again before it reaches the end of the body 

 into what is known as the large intestine, or colon. As in other ani- 

 mals, the alimentary canal is nuicli longer and more capacious in the 

 herbivorous than in the carnivorous kinds. As a general rule the canal 

 is much more capacious in the larva than in the imago state. 



Tlui figure, G, represents the digestive organs of one of the carnivo- 

 rous beetles, Cicindela campestris. a the commencement of the oeso- 

 phagus or gullet ; c the crop ; d the gizzard ; e the stomach or i)riucipal 

 digestive cavity ; / the commencement of the small intestine ; h the 

 large intestine; both of these parts are unusually sliort in this tribe of 

 insects; m m the convoluted vessels wliicharc supposed to represent the 

 liver of the hieher animals. 



Digestive organs of insects explained in 

 tlie text. 



